linux-kernel - Re: [PATCH v5 09/10] PCI: dwc: Small computation improvement

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Message-ID: <d0a96713-9e34-2351-4301-8a2f9039e224@synopsys.com>
Date:   Tue, 17 Apr 2018 20:05:11 +0100
From:   Joao Pinto <Joao.Pinto@...opsys.com>
To:     Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        <bhelgaas@...gle.com>, <lorenzo.pieralisi@....com>,
        <Joao.Pinto@...opsys.com>, <jingoohan1@...il.com>, <kishon@...com>,
        <robh+dt@...nel.org>, <mark.rutland@....com>
CC:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v5 09/10] PCI: dwc: Small computation improvement

Às 3:34 PM de 4/17/2018, Gustavo Pimentel escreveu:
> Replaces a simple division by 2 to a right shift rotation of 1 bit.
> 
> Probably any recent and decent compiler does this kind of substitution
> in order to improve code performance. Nevertheless it's a coding good
> practice whenever there is a division / multiplication by multiple of 2
> to replace it by the equivalent operation in this case, the shift
> rotation.
> 
> Signed-off-by: Gustavo Pimentel <gustavo.pimentel@...opsys.com>
> ---
> Change v1->v2:
>  - Nothing changed, just to follow the patch set version.
> Change v2->v3:
>  - Nothing changed, just to follow the patch set version.
> Changes v3->v4:
>  - Added a small explication to the log description.
> Changes v4->v5:
>  - Nothing changed, just to follow the patch set version.
> 
>  drivers/pci/dwc/pcie-designware-host.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/dwc/pcie-designware-host.c b/drivers/pci/dwc/pcie-designware-host.c
> index 5a23f78..fc55fde 100644
> --- a/drivers/pci/dwc/pcie-designware-host.c
> +++ b/drivers/pci/dwc/pcie-designware-host.c
> @@ -332,8 +332,8 @@ int dw_pcie_host_init(struct pcie_port *pp)
>  
>  	cfg_res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "config");
>  	if (cfg_res) {
> -		pp->cfg0_size = resource_size(cfg_res) / 2;
> -		pp->cfg1_size = resource_size(cfg_res) / 2;
> +		pp->cfg0_size = resource_size(cfg_res) >> 1;
> +		pp->cfg1_size = resource_size(cfg_res) >> 1;
>  		pp->cfg0_base = cfg_res->start;
>  		pp->cfg1_base = cfg_res->start + pp->cfg0_size;
>  	} else if (!pp->va_cfg0_base) {
> @@ -377,8 +377,8 @@ int dw_pcie_host_init(struct pcie_port *pp)
>  			break;
>  		case 0:
>  			pp->cfg = win->res;
> -			pp->cfg0_size = resource_size(pp->cfg) / 2;
> -			pp->cfg1_size = resource_size(pp->cfg) / 2;
> +			pp->cfg0_size = resource_size(pp->cfg) >> 1;
> +			pp->cfg1_size = resource_size(pp->cfg) >> 1;
>  			pp->cfg0_base = pp->cfg->start;
>  			pp->cfg1_base = pp->cfg->start + pp->cfg0_size;
>  			break;
> 

Thanks Gustavo!

Acked-by: Joao Pinto <jpinto@...opsys.com>